Lengauer, Christoph School of Medicine, The Johns Hopkins University, Baltimore, Maryland.
Last reviewed:June 2019
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- Effect on gene expression
- Role in cancer
- DNA hypomethylation
- DNA hypermethylation
- Diagnostic and therapeutic implications
- Related Primary Literature
- Additional Reading
The addition of a methyl group (—CH3) to certain nucleotides in genomic DNA, which is a process having important effects on gene expression. Deoxyribonucleic acid (DNA) methylation, that is, the addition of a methyl group to the DNA molecule, is an important genetic modification and is involved in gene regulation. Besides adenine, guanine, cytosine, and thymine (which are the four bases that spell out the primary sequence of genomic DNA), DNA methylation produces a fifth base called methylcytosine. Methylcytosine is a covalent modification of DNA that is replicated when the cell divides. The enzymes that can add a methyl group to the cytosine ring to form methylcytosine (Fig. 1) are called DNA methyltransferases (DNMTs). In humans and other mammals, this type of DNA modification is imposed only on cytosines that precede a guanosine in the DNA sequence (the CpG nucleotide). In simple organisms, such as yeast and Drosophila, there is little or no DNA methylation. See also: Deoxyribonucleic acid (DNA); Enzyme; Genetics; Genomics; Nucleic acid; Nucleotide
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